From cbf01f738474c26992076e0a6784f82fa94159a0 Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@victoriametrics.com>
Date: Thu, 7 Oct 2021 13:17:20 +0300
Subject: [PATCH] app/vmselect/promql: substitute rollupFuncsCannotAdjustWindow
 with rollupFuncsCanAdjustWindow

The list of functions, which can adjust lookbehind window is more limited than the rest of functions,
so it is better from maintainability and readability PoV using the allowlist instead of blocklist.
---
 app/vmselect/promql/rollup.go | 53 ++++++++++++++---------------------
 1 file changed, 21 insertions(+), 32 deletions(-)

diff --git a/app/vmselect/promql/rollup.go b/app/vmselect/promql/rollup.go
index e569add97d..3056c73bf1 100644
--- a/app/vmselect/promql/rollup.go
+++ b/app/vmselect/promql/rollup.go
@@ -145,37 +145,26 @@ var rollupAggrFuncs = map[string]rollupFunc{
 	"rate_over_sum":       rollupRateOverSum,
 }
 
-var rollupFuncsCannotAdjustWindow = map[string]bool{
-	"changes":             true,
-	"delta":               true,
-	"holt_winters":        true,
-	"idelta":              true,
-	"increase":            true,
-	"predict_linear":      true,
-	"resets":              true,
-	"avg_over_time":       true,
-	"sum_over_time":       true,
-	"count_over_time":     true,
-	"quantile_over_time":  true,
-	"quantiles_over_time": true,
-	"stddev_over_time":    true,
-	"stdvar_over_time":    true,
-	"absent_over_time":    true,
-	"present_over_time":   true,
-	"sum2_over_time":      true,
-	"geomean_over_time":   true,
-	"distinct_over_time":  true,
-	"increases_over_time": true,
-	"decreases_over_time": true,
-	"increase_pure":       true,
-	"integrate":           true,
-	"ascent_over_time":    true,
-	"descent_over_time":   true,
-	"zscore_over_time":    true,
-	"first_over_time":     true,
-	"last_over_time":      true,
-	"min_over_time":       true,
-	"max_over_time":       true,
+// VictoriaMetrics can increase lookbehind window in square brackets for these functions
+// if the given window doesn't contain enough samples for calculations.
+//
+// This is needed in order to return the expected non-empty graphs when zooming in the graph in Grafana,
+// which is built with `func_name(metric[$__interval])` query.
+var rollupFuncsCanAdjustWindow = map[string]bool{
+	"default_rollup":         true,
+	"deriv":                  true,
+	"deriv_fast":             true,
+	"ideriv":                 true,
+	"irate":                  true,
+	"rate":                   true,
+	"rate_over_sum":          true,
+	"rollup":                 true,
+	"rollup_candlestick":     true,
+	"rollup_deriv":           true,
+	"rollup_rate":            true,
+	"rollup_scrape_interval": true,
+	"scrape_interval":        true,
+	"timestamp":              true,
 }
 
 var rollupFuncsRemoveCounterResets = map[string]bool{
@@ -287,7 +276,7 @@ func getRollupConfigs(name string, rf rollupFunc, expr metricsql.Expr, start, en
 			End:             end,
 			Step:            step,
 			Window:          window,
-			MayAdjustWindow: !rollupFuncsCannotAdjustWindow[name],
+			MayAdjustWindow: rollupFuncsCanAdjustWindow[name],
 			LookbackDelta:   lookbackDelta,
 			Timestamps:      sharedTimestamps,
 			isDefaultRollup: name == "default_rollup",